Osteoarthritis and Cartilage

Glucosamine modulates chondrocyte proliferation, matrix synthesis, and gene expression

S. Varghese Ph.D., P. Theprungsirikul B.S., S. Sahani B.S., N. Hwang B.S., K.J. Yarema Ph.D. and J.H. Elisseeff Ph.D.

Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21218, USA

Summary:

The therapies that currently exist for improving general joint health and for treating the symptoms of the degenerative disease osteoarthritis (OA) include the use of anti-inflammatory and pain relieving drugs. However, it has also been hypothesized that the dietary supplementation of "chondro-protective" components such as glucosamine (GlcN) and chondrotin sulfate (CS) could be used to treat OA by stimulating cartilage regeneration. In this present study, Varghese et al. sought to identify what optimal concentration of GlcN (if one such concentration did exist) had a significant effect on chondrocyte proliferation, matrix production, a gene expression in both monolayer (2D) and three-dimensional (3D) culture conditions. They attempted to accomplish this task by evaluating the effects of various amounts of GlcN on primary bovine articular chondrocytes (BAC) and by demonstrating how the responses of the cells differ between the two culture conditions. Reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR were used to examine the impact of GlcN on gene expression in both culture conditions, specifically aggrecans and collagen type II. Yet in order to accurately evaluate the effects of GlcN on cartilage matrix production in the 3D culture conditions, it was also necessary to perform histology, immunofluorescent staining and biochemical analyses.

Noticeable differences in both cellular morphology and the microenvironment surrounding the cells were observed between the 2D and 3D culture conditions. The authors suggest that these discrete differences in GlcN tolerance may be attributed to the various niches the two conditions provide to the cells. In particular, the 3D hydrogels provided a structural environment that was more similar to native articular cartilage. For instance, incubation of 3D constructs with 2mM GlcN-medium resulted in the highest cartilage specific matrix production, GAG and collagen type II. However, as in 2D culture conditions, a decrease in cell proliferation and adverse effects on chondrocyte matrix production with increasing GlcN concentrations was still observed in the 3D culture conditions. GlcN was also found to upregulate TGF-beta1 mRNA levels in a dose-dependent manner in both the 2D and 3D culture conditions. Moreover, based on their findings, the authors emphasized that chondrocytes needed to be given sufficient time to adhere onto the culture dish (i.e., in monolayer culture conditions) in order to even survive at high GlcN concentrations. TGF-beta1 is known to stimulate the collagen production of articular chondrocytes and is considered to regulate cartilage fracture repair by extracellular matrix production.

Significance:

Various studies that have investigated the effect of agents such as glucosamine on cartilage regeneration report mixed results; some promising, and others not, making this subject highly controversial. The present study, however, provides additional evidence that prolonged exposure of primary chondrocytes to optimal GlcN concentrations increases matrix production. The authors also indicate that this may be the first study of its kind that demonstrates GlcN mediated up-regulation of TGF-beta1 in chondrocytes. The authors propose that the increased production of extracellular matrix can possibly be explained by the GlcN mediated up-regulation of TGF-beta1. By promoting the expression of TGF-beta1, the authors hypothesize that optimal amounts of GlcN can preserve cartilage tissue and promote its repair upon damage. Hence, this study paves the way for the development of better clinical strategies for cartilage repair involving localized and controlled release of GlcN.